A continuing problem in the application of liquid materials such as, for example, paints, fertilizers, herbicides, insecticides and other treatment liquids, including solutions and suspensions, is that of insuring a desired, uniform application. Clearly, non-uniform application will provide non-uniform results and such results will vary from ineffective treatment to excessive treatment which can be both costly and damaging in some uses, such as in agricultural sprays.
Various attempts have been made to overcome these problems, as seen, for example, in U.S. Pat. Nos. 3,902,667 and 4,260,107. Such systems generally employ pumps and it has been found that pumps do not always deliver a constant volume because of several factors such as wear, clogging or a variation in the power to the pump itself. Electrically controlled systems, because of the possibility of igniting volatile carriers, are not desirable for safety reasons, particularly when liquids are to be sprayed in relatively confined spaces.